1. Field of the Invention
The present application relates to multilayered polyimide films, and more particularly to polyimide film having a low dielectric constant.
2. Description of the Related Art
Electronic products require increasingly thinner, smaller and lightweight print circuit boards (PCB). Moreover, because wireless internet and communication devices operate at higher frequency, efforts have been made to develop circuit boards capable of high transmission rates. Basic requirements for the materials of the circuit boards include the ability to transfer data at a high rate, and prevent data alteration or interference during transmission.
It is known that the transmission speed in semiconductor devices is mainly limited by the occurrence of delay between metal wires carrying the signals. In order to reduce the delay in signal transmission, an insulating layer having a low dielectric constant can be disposed between the wires, which can reduce capacitance coupling between the wires, enhance the operation speed and reduce noise interference. The insulating layer can block the flow of an electric current, and a lower dielectric constant can reduce the occurrence of undesirable stray capacitance. Moreover, the insulating material should have a dissipation factor that is as small as possible to minimize waste of electric energy. In other words, the high-frequency circuit boards need to have a low coefficient of thermal expansion (CTE), low dissipation factor (Df), and stable and low dielectric constant (Dk).
To satisfy the aforementioned requirements, the material selected for making the board needs to exhibit a low dielectric constant, low thermal expansion, ability to form a multilayered structure, and good heat and chemical resistance. In this regard, polyimide has been widely used to make printed circuit boards. However, facing the tendency of size reduction of the products, there is still a need for a polyimide film having improved dielectric constant and capable of meeting the requisite CTE characteristics.